text:
Will this simple equation (pic attached) produce a rough estimate of the top speed of a prop driven aircraft?
Calculating the approximate top speed of a vehicle is straightforward.
$v = \sqrt[3]{\frac{2P}{c \cdot D \cdot A}}$
where

v = velocity of the vehicle
P = power of the engine
c = coefficient of friction
D = density of the air
A = the area of the front of the vehicle

Using this equation you can get a rough idea of the top speed of a car if you know its engine power, the body’s coefficient of friction and the area of its front profile.
Is it possible to use this same equation to determine an approximate top speed for subsonic aircraft?  No doubt engineers at Boeing have to account for 100 additional variables, but is it good enough to produce a decent approximation for props that fly less than 500mph?
Also does the picture I attached below show the correct way to account for variables $A$ and $c$?

If $c$ represents the friction along the entire surface of the aircraft does this suggest that all things being equal an aircraft with twice the surface area would have twice the coefficient of friction?  Or am I looking at $c$ incorrectly?

@Hobo Sapiens I believe decent propeller efficiency is around .7 so I could use that for an estimate.  But doesn't induced drag drop the faster a plane travels?  So induced wouldn't be a significant factor in top speed?

The short answer is no, that will not give you a very accurate estimate. As other mentioned, your equation does not include lift. Given some basic engine specs and aerodynamic properties, the top speed for aircraft can be estimated by determining the intersection of required power and available power. Available power is based on selected engines and propellers, and required power is based on the wing loading, lift coefficient, and other parameters that describe the amount of power required to sustain minimum lift.

Will this simple equation produce a rough estimate of the top speed of a prop driven aircraft?

Yes, but only with the correct reference area.
You are on the right track, but need to consider what a friction coefficient is. A coefficient is a dimensionless value which, in the case of friction, needs to be multiplied with an area and a dynamic pressure to yield a force. Equating this force to the available thrust does indeed produce a good estimate of maximum speed.
However, just applying some friction coefficient will not suffice. You need to know how much of the surface has a laminar boundary layer, what the local roughness and the Reynolds number of the flow are and you need to add correction factors for Mach and relative thickness, as demonstrated in this answer. And the method only works for sleek shapes - a blunt base like on the Shuttle will add a lot of pressure drag which is neglected by this method.
If you have done all that, use the full wetted surface of the whole aircraft (not just its wing surface!) for the drag calculation. The front profile will not help you - now you need the top and side view to arrive at a useable result. For good measure, you should also add a correction factor to account for surface imperfections (gaps, rivet heads, antennas …).
But lift is not considered, you might say. Yes, but drag due to lift is insignificant at top speed for well motorized aircraft. If you desire a more precise result, of course you should include induced drag.

If c represent the friction along the entire surface of the aircraft does this suggest that all things being equal an aircraft with twice the surface area would have twice the coefficient of friction?

No. The coefficient will stay the same, but the reference area will double, so the force will double, too.

All fascinating!  Now the coefficient makes sense.  It needs a reference area.  But I have a followup question in regards to wetted area.  In your answer to this question https://aviation.stackexchange.com/questions/50462/is-there-an-aerodynamic-force-that-would-keep-this-experimental-ww2-era-prop-fro  you mentioned that the surface area would be reduced to 70.7% of the original.  But in your equation I don't see reference to 70.7%, only 1/2.  Is that being accounted for in some other way?  Or maybe your equation was just a rough estimate?  Thanks so much this is very helpful!

if the Space Shuttle's blunt shape produced additional pressure drag is that why aircraft like the HE-219 were so narrow?  Of was the 219 narrow simply to reduce the wetted area?  You can see an image of it here.  https://airandspace.si.edu/collection-objects/heinkel-he-219-2r4-uhu-eagle-owl

@DR01D: The size comment referred to the length change. An aircraft with 70.7% size will have half the area. And yes, the reduction in frontal area was believed to be key to drag reduction 70 or 80 years ago, but does not result in the smallest wetted area. Some two-engine designs even moved the engine instruments into the nacelles in order to reduce the cockpit size.

The key aspect of flight is lift and your automobile equations don't have it so no, you can't estimate any speed for the subject aircraft. There is no weight, lift coefficient, wing span, or wing area. A coefficient of friction applies to surface area not to frontal area, where you need a drag coefficient. Coefficients do not change when applied to a larger reference area.
Here is a NASA page dealing with lift:
https://wright.nasa.gov/airplane/lifteq.html


text:
How are "preferred routes" assigned if there is more demand than capacity on a route?
There might be multiple routes, belonging to the “Preferred Routes” class, connecting the same pair of airports.
However some of them might be more appealing for non-urgent circumstances such as less turbulence, more favorable winds, etc. Therefore there will be a route (as long as I understand) that is the desired one by many airlines at the same time.
Let’s suppose we have airlines A, B, and C requesting a flight on route x, but the capacity is one per route, or stated another way, only one of the three airlines can take the route and the other two must choose another route.
Which is the protocol followed to decide if the route x is assigned to A, B, or C?

Why wouldn't they be able to fly one after another? Or at different levels?

It's hard to imagine, for the comments posted above, that a route can be so saturated that it isn't available. Separation is just a few miles horizontally and add low as 500 feet vertically. The real problem is sequencing into or out of airports.

Understood, you are right, I can reformulate my doubt in the following way: which one would have preference to take off first and why? Referring to the saturation, I don't know how in practice is implemented but in the mathematical models there is what is called the "cell occupancy limit" that roughly limits the total number of flights allowed in a certain region, which could cause that after the first flight the cell occupancy reaches its threshold and the model doesn't let more flights to traverse the area.

Dispatchers file flight plans in the national airspace system. Each flight plan is given a "slot" for departure (and for arrival). The flight needs to depart within this slot or it may be put in a waiting list for another slot. They can also file "suboptimal" flight plans to take less desirable routes for better departure slots.

Related: FAA traffic flow management for the US and ETFMS for the EU.  Article: Air traffic flow management problem with enroute capacties. And Can airlines schedule more flight arrivals than the airport capacity?

RVSM was implemented to reduce the vertical separation above flight level (FL) 290 from 2000-ft minimum to 1000-ft minimum. It allows aircraft to safely fly more optimum profiles, gain fuel savings and increase airspace capacity. The process of safely changing the separation standard required a study to assess the actual performance of airspace users under the old vertical separation standard of 2000-ft and potential performance under the new standard 1000-ft.  https://www.faa.gov/air_traffic/separation_standards/rvsm/

Air traffic services (at least in the US) are handled on a first come first serve basis. That's the overarching protocol. Beyond that, it's situation dependent.
In the air, controllers give pilots what they want if possible. In practice the situation is quite fluid. Maybe all three can't go on the same path now, but in a minute there will be enough clear airspace to make it happen. Or maybe they go on a route very close to but not exactly what they requested.
If (for some reason like a prominent jet stream) many airplanes are filing the same (or very similar) flight plans so that certain airspace will be overwhelmed, there is an entire division of the FAA dedicated to deciding where and when aircraft need to be rerouted. Here's some info @mins linked to in a comment.
Also, your question seems to assume competing airlines. For all ATC cares, A, B, and C could all be flights of the same airline.

Preferred routes as well as the Tower Enroute Control (TEC) routes are established to facilitate flight operations between major hubs which alleviates congestion for controllers, providing expedient sequencing for departures and arrivals as well as travel along airways.  This has to do with a number of factors, including terrain, routing navaids and waypoints, airport and airspace configurations and existing arrival and departure procedures.  They are also chosen for specific types of aircraft e.g. Turbojets or turboprops and various onboard navigation equipment e.g. RNAV, GNSS, etc.
You can, at least technically, file any kind of flight plan you like, but if it doesn't use these preferred routes, controllers will likely amend your clearance, routing you along a preferred route of their choosing based on anticipated traffic congestion at both departure and arrival times.  If an urgent situation arises, a pilot can declare this and ATC will work with them to resolve the situation.

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text:
Is prior clearance into Class B airspace revokable?
I was piloting outside of Class B airspace in an area well known for being difficult from which to contact ATC via radio because of mountainous terrain. When I did get cleared into Class B, I was only about a mile outside of Class B airspace. Immediately, another controller took over (different gender / same frequency), revoked the clearance, and said to stay clear of Class B and scolded me for only being one mile outside of Class B. (I complied with that request, never entering Class B – so there was no violation.)
Question: Can you legally be “uncleared” into Class B after receiving a clearance into Class B?
Could you speculate on what may have happened?

Unless you are in an emergency, you are required to comply with all ATC instructions, so yes, a clearance can be revoked. Just like a landing clearance or crossing clearance. The controller shouldn't have scolded you though, you were clear of the airspace, unless you were coming in at a fast rate. Ideally you'd like to get clearance quite a bit before that. I like to contact Class C at least 20 miles out, and for Class B I'd get flight following if possible as I left my origin.

Sure, a clearance can be changed or even revoked. It happens all the time. The traffic situation may change, equipment could fail, an emergency could appear, etc. Air traffic control is extremely dynamic - the work of the controller can change 100% in as little as 5 minutes.

I'd listen to the conversation on liveatc.net and make sure that it really did happen as you recall. If it did, I'd file an ASRS report: as you described it, it seems that the handover from one controller to another wasn't done well. If the second controller "scolded" you then s/he was presumably unaware of the previous clearance issued, and that shouldn't be the case.

@Pondlife It doesn't sound like a frequency change to me. More likely, a supervisor cut in after the other controller already gave the clearance because they weren't comfortable with the potential situation. I hear this happen every once in a while.

@Lnafziger That's an interesting idea, I didn't think of that. But then why would the supervisor scold the pilot if the mistake was on the ATC side? I actually understood it was a controller change, not a frequency change.

@Pondlife I guess that they felt like the pilot waited too long to make the request, even though he hadn't done anything illegal, lol.

Every clearance can be cancelled or revoked, irrespective of the type of clearance.

My speculation on what happened is: The first controller was in training and the second controller was their trainer. The trainee cleared you into the Class B but the trainer though that was a bad idea (perhaps there was traffic nearby they couldn't have kept you away from, or they wanted to teach you a lesson about calling too late, or they thought their trainee was too busy to provide VFR services, or they woke up on the wrong side of the bed that morning) and came on frequency to contradict the trainee's clearance.
When controllers are first hired, and any time they transfer facilities, they have to complete on-the-job training. This is because:

Learning how to control simulated traffic in the schoolhouse is not good enough to let a new controller talk to actual planes with actual people in them making actual crazy requests they never had to deal with in the simulator.
Airspace and procedures are different everywhere. Even if you were the best of the best at your last facility, you don't know all the nuances of the new facility.
Different facilities have different controlling techniques and requirements. It's very possible for someone to transfer from a tower-only flight-school-heavy facility to a radar approach control working commercial traffic into a Class B or even to an enroute center.

That's why you'll sometimes hear a second voice come on frequency and tell you to disregard what the first controller just said. It won't be a supervisor, it'll be a certified controller who is conducting training.

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text:
What are these circles around the propeller?

(Source: www.airliners.net)
These circles I believe are the wing tip vortex formed by the propeller tips or is it just due to the rotation of the propeller. How does this occur?

Ethan. Do yourself a favour. Many people, in many of your questions have pointed out that wings, propellor blades and rotor blades are all the same thing. If you would finally pay attention to this, and learn it, then you would have realised and known that these are tip vortices just like wing tip vortices. The problem is, if you keep asking the same questions and not learning from people trying to help, the help will dry up.

@Simon in my head I pictured the wake on a blade to be different and that confused me to the point of I didnt know what the circles where for.

NP.  So hopefully, you now get the point that wings, propellor blades and rotor blades are all the same thing.  An aerofoil that accelerates air to produce a force.  Different purposes, different shapes, different designs, but all the same thing.

@Simon I do have a good understanding of it now

I've seen that exact picture posted on another question (or possibly answer) somewhere, but can't find it at the moment. This is easily a duplicate of that question, if not 1/2 a dozen others.

They are tip vortices formed by the propeller, just like the wing tip vortices.
The propeller produces thrust, just like the normal wing produces lift. As any wing of finite length produces vortices, the propeller also produces them and that is what you see in the picture.
This is not only limited to propellers. The helicopter rotors also do the same thing.

can these viewed at particular environment like humidity, moisture, fog etc? or special camera needs to be used to capture these vortices, as these are created by all type of propellers in aircraft as well in helicopters.

@Lucky These require no special cameras. These vortices are always formed by the propeller/aircraft but usually become visible in humid conditions.

@Lucky When air is pressurised, it's ability to hold moisture as a vapour reduces and the water condenses out.  In completely dry air, you would never see them.  You would need smoke, dust or some other particulate suspended in the air to see them but when the conditions are right (temperate, humidity and dew point), then water in the air condenses out when under pressure.

@aeroalias No special cameras, but a phone won't do in most circumstances. You'll need to be able to control shutter speed and aperture in order to capture just enough rotations for getting a pretty picture.

Why are these vortices? Vortices are produced by anything in the air that moves pretty much. What you can see on the picture however is actually water vapor or contrails.

The pressure in the core of a vortex (such as that shed at the tip of an operating propeller, rotor, wing or extended flap) is reduced well below ambient pressure. The temperature is also lower than ambient because of the lowered pressure. If the temperature is lowered to the dew point, the water vapour will condense and become visible revealing the vortex core.
This is aerodynamic condensation. It is related to the over-wing condensation sometimes seen during landings and takeoffs in very humid conditions, and around the wings in extreme aerobatic manoeuvres. It is caused by the lowering of pressure and the accompanying lowering of temperature.


text:
Relationship Between Aircraft Thrust and Jet Exhaust Velocity?
What is the relationship between aircraft thrust and jet exhaust velocity & thrust and mass flow.
Actually, my question is how to reduce or decrease jet noise without decreasing the thrust ?

Welcome. You have two different questions, which are both broad. You should split your post into two different ones with appropriate titles and detail with type of engines your are asking for. There are already answers on the site, please explain what is missing, to get better answers, e.g. Why does the Boeing 787 engine nacelle exhaust have such an unusual shape?

And, you question appears to be essentially a duplicate of your last one. It would fit with the flow of SE much better to have edited your original question, which would spawn a series of comments helping you refine it to get it reopened.

Though this post is a duplicate of the original, it does have an answer, as opposed to the (closed) original. Perhaps this question aught to be left open.

The thrust produced is propotional to the exhaust velocity and mass flow, in simple terms. The thrust equation can be written as,
$T$ = $\dot{m}_{e} v_{e} - \dot{m}_{o} v_{o} - (P_{e} - P_{o}) A_{e}$
where, $\dot{m}$ is the mass flow rate $v$ is the velocity, $P$ is the pressure and $A$ is the (exhaust) area. The subscripts 'o' and 'e' denote the freestream and exhaust values respectively.
There are multiple ways to go about noise reduction in aicraft engines, all with some kind of penalty- the Boeing method is to use chevron shaped exhausts (Interestingly, the type chosen is the one with lesser thrust penalty, not the most effective in noise reduction). However, Airbus has cited higher fuel consumption as the main reason for them not using it. Airbus uses acoustic liners in the engine to reduce noise:

The thrust reverser structure was acoustically treated along approximately
  half of its internal surface. It was clear that increasing this acoustic area would increase the acoustic sound absorption and hence decrease the overall measurable exhaust noise.


text:
Which is a longest flight in the world?
Which is a longest flight in the world?

@fooot he does not specify commercial flight or not

See also What is the record length of time for single-occupant flight?, How far can Boeing 777-200LR fly?, What are the factors that limit how long an aircraft can stay aloft?

Any answer could go out of date and no longer be a correct answer.

I think the Voyager probe or something...

Longest scheduled passenger flight in history is Singapore SQ21/22 between New York (Newark) and Singapore with distance 8285nm by A340-500, the service was dropped in 2013, but Singapore airline planned to reintroduce the route using A350.
Longest non-scheduled passenger flight record is archived by a B777-200LR on 9 November 2005, from Hong Kong to London eastwardly, travelled 11664nm.
Longest fueled Flight endurance record is archived by Robert Timm and John Cook from 4th December 1958 to 7th February 1959, using Cessna 172. And the longest longest Non-refueled record is archived by Dick Rutan and Jeana Yeager from 14th to 23rd December 1986, using Rutan Voyager.


text:
How does a helicopter rudder work?
So occasionally I will be flying my rc helicopter and I turn it left to right (rudder) but see nothing moving on the helicopter. On an aircraft there is a vertical stabilizer that has a moving rudder. So how does a helicopter work? The same thing occurs with my quadcopter.

See also alternatives to tail rotors, specifically the coaxial design, and hover.

In helicopter, the yaw control is usually obtained by adjusting the pitch of the tail rotor, that changes the 'thrust' produced by the tail rotor; this rotates the helicopter about its yaw axis.

Source: cfidarren.com
In case of helicopters without a tail rotor, the yaw control is obtained in different ways. The NOTAR used a method similar to the tail rotor, by varying the thrust. In case of tandem rotors (like Chinook) , the yaw control is obtained by differential lateral cyclic.

Source: tech-mp.com
The quadcopters obtain yaw control by adjsuting the speed of the rotors. In quadcopter, two rotors (say 1 and 3) rotate in one direction, while the other two (2 and 4) move in the other. By slowing down 1 and 3 while speeding up 2 and 4, you can make the quadicopter yaw to the left. The torque of 2 and 4 spinning to the right makes the body spin to the left. Conversely, by slowing down 2 and 4 while speeding up 1 and 3, the quadcopter yaws to the right.

Source: safaribooksonline.com
In case of coaxial helicopters like the Kamon Ka-25, the yaw control is obtained by varying the torques (i.e. by varying the pitch) of both the main rotors simultaneously in opposite direction.

Source: simhq.com
Coaxial helicopters (like Kamov Ka-25) do have movable rudders like aircraft for use in forward flight as it reduces the main rotor adjustment required and is more effective.

Ka-25 rudder, image from travelforaircraft.wordpress.com
The image below shows the control methods used in different types of helicopters.

Image from unicopter.com, credited to Rotary-Wing Aerodynamics.

So basically the blades lean to the right side and the helicopter turns to the right side like a rudder

@Ethan No!  The blades don't "lean".  The rotor disk is titled, so the thrust vector now has a horizontal component.  It's the horizontal component which causes movement in the Y-axis or rotation around the Z-axis.  This has been explained several times in questions you have asked.  If there is anything in this comment that you do not understand, ask, since if you do not understand this comment, then you do not understand how helicopters fly.

Helicopters do not have rudders.
They have tail rotors.  You yaw left and right by varying the pitch of the blades, therefore varying the thrust they generate to counter the torque from the main rotor.
From Wikipedia.

Some helicopters use "NOTAR" (NO TAil Rotor) or ducted fans.  The duct is rotated with the anti-torque pedals which varies the horizontal component of the thrust.

Quadcopters yaw by changing the speed, and therefore the thrust, of the rotors individually to "bend" the quadcopter.

http://uav-society.blogspot.co.uk/2014/06/quadcopter-mechanics.html

Do you know of any picture that could show this

@Ethan Have you moved the rudder stick when your helicopter is on the ground and the rotor isn't spinning? Isn't there a servo somewhere connected to the tail rotor with a linkage on your helicopter?

There are a few helicopter designs I've seen that do have moving rudder surfaces. These tend to be twinrotor designs with no tail rotor, like the Ka-50 Hokum (which has an all-moving rudder). At high forward speed, it's more efficient to use a rudder surface to yaw than to alter relative torque of the main rotors. For the same reason, the AH-64 Apache has an all-moving stabilator, which helps to pitch the aircraft in combination with blade pitch to avoid stressing the rotor blades or hub at speed. None of these would apply to most RC helicopters.


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Which "pilotless aircraft" did the authors of the 1944 Chicago convention have in mind?
The Convention on International Civil Aviation (a.k.a. the "Chicago convention"), includes right from its first version, signed in 1944, an article about "pilotless aircraft". The article in question reads:

Pilotless aircraft
Article 8
No aircraft capable of being flown without a pilot shall be flown
without a pilot over the territory of a contracting State without
special authorization by that State and in accordance with the terms
of such authorization. Each contracting State undertakes to insure
that the flight of such aircraft without a pilot in regions open to
civil aircraft shall be so controlled as to obviate danger to civil
aircraft.

The original text is available here.
I would guess that language like that (which it takes time and effort to produce) will not get included in an international treaty without a reason.
So the question is, which aircraft did the authors of article 8 have in mind in 1944?

The only pilotless aircraft I can recall from that era were barrage balloons, but those are tethered and don't actually navigate, so I doubt that's what they had in mind. I would expect they were simply anticipating the foreseeable.

The V1 was from that timeframe.  https://en.wikipedia.org/wiki/V-1_flying_bomb

The US armed forces began experimenting with "drones" in the 1930s: https://en.wikipedia.org/wiki/History_of_unmanned_aerial_vehicles. While many hobbyists detest the use of the term "drone" to describe radio controlled aircraft the term "drone" as applied to unmanned aircraft originated with the early US Navy research in the 30s and 40s. They mostly ended up being used for target practice but at least two programs were designed to develop pilotless kamikaze aircraft (one piloted remotely by TV signal and one piloted by pigeons)

Note that the article says that

No aircraft capable of being flown without a pilot

At that point of time there were a number of radio controlled aircraft which could be flown without a pilot on board (for example, the RP series aircraft and OQ-2 Target drone, of which thousands were made). The authors of convention most probably had these in mind when they frame the article 8.
This ICAO document on Unmanned Aircraft Systems also points in the same direction:

4.3  Article  8  details  conditions  for  operating  a  “pilotless”  aircraft  over  the  territory  of  a  contracting  State.  To  understand  he  implications  of  this  Article  and  its  inclusion  from  the  Paris  convention  of  1919  (Article  15)  into  the  Chicago  Convention  of  1944,  the  intent  of  the  drafters  must  be  considered.  Remote-control  and  uncontrolled  aircraft  were in existence at the time, operated by both civil and military entities. “[A]ircraft flown without a pilot” therefore refers to  the  situation  where  there  is  no  pilot  on  board  the  aircraft.  As  a  consequence,  any  RPA  is  a  “pilotless”  aircraft,  consistent with the intent of the drafters of Article 8.

(emphasis mine). So, the authors of the 1944 Chicago convention most probably had radio controlled aircraft in mind.


text:
How does trim work on an A320?
In the very interesting answer from Jan Hudec to a question about the various flight control computers on Airbus planes, two different means to trim the aircraft are mentioned: The stabiliser and the elevator.
How does this work in practice? How is the aircraft trimmed in flight, both as seen from the flight deck (i.e., the user interface to the pilots) and as actual input to the control surfaces?

Are you asking about trim in normal cruise phase under normal law with all systems operating normally or some other flight phase or condition or flight law?

@RedGrittyBrick Let's stick to normal law, which after all, er, normal. It would be nice to know if there are differences in how it works for different phases (or conditions) of flight, though.

The faster an aircraft is, the wider range of elevator deflections it needs. And so do aircraft with large change of weight (amount of fuel used) during flight. However larger elevator deflection causes higher drag. It is more efficient to move the whole horizontal stabilizer instead. Therefore jet aircraft generally have the forward part of the horizontal stabilizer movable.
Now it would be possible to simply have the whole stabilizer move. And supersonic aircraft generally have just that. It is called stabilators. However having the stabilizer split lends itself to elegant solution for trim.
This takes advantage of the fact, that the aerodynamic forces tend to put the elevator in the position of lowest drag almost straight (slightly bent in direction of less lift) behind the forward part. So when the forward part is moved, the lift changes without changing the force on the elevator. So the elevator is used for the small adjustments where the elevator is intended to return to the neutral position, which the aerodynamic forces help with, and the stabilizer is used to trim for current airspeed.
In aircraft with mechanical controls, the elevator force (or a fraction of it via power drive) acts directly back on the control column and the pilot can feel it, while the horizontal stabilizer is actuated via mechanism that holds selected position (may be electrical with jack-screw like on DC-9 or hydraulic, but with no feedback) and connected to the trim, which is usually pair of large wheels on the sides of the centre console.
Now in Airbus A320 and all newer models the side-stick does not have mechanical link and the pilot does not feel the force on the elevator anyway. In normal law, the ELACs automaically adjust the elevator and stabilizer so that with side-stick in neutral position, the aircraft maintains 1 G vertical acceleration and therefore straight flight (at any flight path angle). Since the trim wheel does have direct mechanical link, it turns as the ELACs (or SECs) adjust trim.
However the distinction between elevator and trim is still useful in case of failure. When the system degrades into direct law, the side-stick position corresponds to the elevator deflection and the trim wheel position corresponds to the stabilizer position. Since the side-stick still returns to neutral position, the distinction of using the elevator for momentary adjustments and trim to balance the aircraft to fly (approximately) straight at current speed holds (just because the side-stick is spring-loaded, the force needed to deflect it does not increase with speed as it does for mechanical controls).

Great answer, thanks! I now also see why the trim wheels are implemented as they are.

Why the faster the wider the range? I thought the range of movables was sized by low speed,where due to small dynamic pressure we have small efficiencies...

@GHB, the size is determined by need for sufficient authority at low speed. But on faster plane it needs to adapt to larger range of angles of attack.

@JanHudec sorry I still don't get it! The Aero pitching moment that the elev can generate will be dictated by both the size of it and the deflection of it:  $M_a = q S b Cm_{\delta_{elev}} \delta_{elev} $, p dynamic pressure, S wing area, b wing span, $ \delta_{elev} $ elev deflection. The magnitude of the control derivative $Cm_{\delta_{elev}}$ will be given by the size of the elevator itself ($Cm_{\delta_{elev}} \leq Cm_{\delta_{stab}} $ ).
Do you mean: on faster aircraft, being the low speed constraining, the elev shall provide a wider range of deflect than considering high speed only?

I see that the Airbus cockpit has trim wheels, but they seem to be there for information only, they have no cranks like the 737. Can they be adjusted manually in direct law? If yes, how? Buy grabbing the wheel? Isn't it inefficient compared to the cranks? OTOH, I see the newer cockpits have no trim wheels at all.

@RustyCore, Airbus has trim wheels and they are to be adjusted manually in direct and mechanical laws (mechanical law was deleted from A380 onward). Unlike 737 they are hydraulic though, so they are easier to turn and need fewer revolutions.

It is fully hydraulic, the active power is the hydraulic even when you act directly on the wheels, that’s why there is no handles to the Wheels, the wheels will control a valve block to drive the screw.
There is no thumb switch to operate the trim, when you move the stick the elevators are operated for short term action to get the desired load factor, followed by the trim which moves automatically to maintain that load factor, and replaces at long run the elevators effect, thus at long run the THS and the elevators are aligned which reduces the drag.

This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post. - From Review

@Sean, ok, I added a useful information just now to complete the answer.


text:
When is a sailplane a sailplane?
A simple question that I could not find an answer to:
When is a sailplane a sailplane (from a regulatory point of view), especially a powered one of the TMG (touring motor glider) variety?
EASA has some quite simple definitions, presumably modelled over the similar ones from ICAO, according to which:

‘Sailplane’ means a heavier-than-air aircraft that is supported in
flight by the dynamic reaction of the air against its fixed lifting
surfaces, the free flight of which does not depend on an engine.
‘Powered sailplane’ means an aircraft, equipped with one or more
engines having, with engine(s) inoperative, the characteristics of a
sailplane.
‘Touring motor glider’ means a specific class of powered sailplane
having an integrally mounted, non-retractable engine and a
non-retractable propeller. It shall be capable of taking off and
climbing under its own power according to its flight manual.

From this simple chain of definitions, it would seem that, for instance, a Cessna 152 could be classified as a TMG: It can take off and climb under its own power, and with the (non-retractable) engine inoperative it will do free flight sustained by its "fixed lifting surfaces", otherwise known as wings.
Since a Cessna 152 is not normally seen as a glider, I presume that there are more rules that need to be respected before a plane can be called a glider (or sailplane in EASA's classification).
I know that CS-22 contains the specifics, but is there a simple set of rules to determine if an aircraft belongs to the class of (powered) sailplanes as opposed to normal aeroplanes?

I'd guess that the "free flight which does not depend on an engine" is where the definition does not apply. The Cessna is capable of gliding safely down to a controlled landing, but cannot be sustained in flight indefinitely by use of thermals and ridge lift.

@IanF1: How long is "indefinitely", for sailplanes? Thirty hours? Ten hours? Two hours? How long can a Cessna theoretically remain aloft under ideal conditions? That's some fuzzy gray area there that really would need precise definition.

Yes i agree, which is why I put it in a comment :) I guess another way of looking at it is that in the cessna you'd be making a mayday call and looking for somewhere to land, rather than looking for thermals etc. But again that's about SOP rather than what's physically possible. Peter's answer about sink rate is clearly the way to go here.

The Cessna 152 doesn't meet the quoted EASA definition of a TMG. This is because it doesn't qualify as a "class of powered sailplane" because it doesn't have "the characteristics of a sailplane" namely "the free flight of which does not depend on an engine" - It seems to me the quoted definitions are adequate to distinguish aircraft like the 152 from sailplanes, powered sailplanes and touring motor gliders.

There are indeed several steps between a pure glider and a powered aircraft. The criteria were historically quite simple:

Gliders with an auxiliary engine, which is just for getting them home in adverse weather, but not powerful enough for take-off. The propeller is in almost all cases retractable, so their aerodynamics is identical to their pure glider version, apart from a slightly higher minimum wing loading.
Motorgliders with an engine powerful enough for autonomous take-off, but with aerodynamics which gives them less than 1 m/s minimum sink with the engine switched off. This minimum sink decides if they are still powered gliders. This would be the TMG category.
Powered aircraft with an unpowered minimum sink speed in excess of 1 m/s. The Cessna 152 belongs into this category.

With the introduction of glassfiber motorgliders with their higher wing loading, the minimum sink rule could not be maintained, and manufacturers lobbied for a change in regulations. As it currently stands, CS-22 defines sailplanes to be within its scope if the maximum weight is below 750 kg. Powered sailplanes must not have more than two occupants, weigh 850 kg or less and have a span loading of 3 kg/m² (mass per span squared) or less.
CS 22.71 restricts minimum sink in unpowered flight to 1.0 m/s for single seaters and 1.2 m/s for two seaters.
Please note that suitable instrumentation should also be added for a motor glider to be counted as a sailplane, such as a variometer.

Thanks - the requirement for minimum sink rate and wing loading effectively ensures that "normal" sailplanes (powered or not) will be different from other planes. The need for a variometer won't be in the regulations, though, if I understand them correctly.

The easiest way to find out for a particular aircraft type is to check its (TCDS) Type Certificate Data Sheet. In it, you will find its certification basis and airworthiness category (CS-22, CS-23, CS-25, CS-VLA etc).
EASA TCDS's are available for free at:
https://easa.europa.eu/document-library/type-certificates
FAA TCDS's are also available for free at:
http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/MainFrame?OpenFrameSet
If you search the FAA TCDS database for Cessna 152, you will find its certification basis is CS-23 ("Normal, Utility, Aerobatic and Commuter Aeroplanes") and not CS-22 ("Sailplanes and Powered Sailplanes"). To determine whether Cessna 152 could actually be type certified iaw CS-22 one would have to consult CS-22. I highly suspect that it contains weight limits, maximum energy and/or other limits that would bar the Cessna 152.
For your reading pleasure:

FAA TCDS 3A19 (C152)
EASA TCDS A.074 (Duo Discus T)
EASA CS-22
EASA CS-23


text:
Why are some aircraft finally announced to the public?
What is the reasoning for telling the public about an aircraft like the f-22 for example.source:(commons.wikimedia.org)
Isn't the point of keeping an aircraft top secret so other countries won't know about this new technology this company came up with? Revealing this kind of technology to the public would allow other countries to know about it and design something better. The f-22 was released to the public in 2005, which gave China a good amount of time to try to design something better called the J-20.(better in certain areas)source:(www.globalsecurity.org)

Security by obscurity is hardly a successful tactic.

Why is this on hold? Sure seems on-topic to me. I vote to re-open. And I say good question, good answers.

@TomMcW It's a question about military security, not aviation. The answer would be no different if the question was about a battle tank rather than an aircraft.

@David Agreed that the concepts applied do apply to all military secrets, but, man, that seems awfully picky to me. It does reference specific aircraft. If we off-topic this we'd have to off-topic a whole lot of good questions on here. If there was a military SE I'd say it could be migrated but there isn't a more appropriate home for it.

An aeroplane is a large, highly visible object. Unless you're going to fly it only at night from remote airfields and can guarantee radar invisibility, the world will find out about it sooner or later. (Note that the F-117 Nighthawk is rumoured to have been in service for several years before it became public knowledge, flying under exactly these restrictions)
There will also be large holes in public finance where funds have been used to pay for development, so anyone with an interest in seeing what a government has been up to can find out about such projects from public records (yes - we know that black projects can be hidden, but there is a limit to what one can get away with)
It's also easier to keep really important secrets if they're relatively small. Tell the world you have a bright shiny new aeroplane, with a whizz-bang rocket system, and the world won't look for the fancy gadget on the instrument panel that vaporises enemy jets electronically at a range of 500 miles. (Any resemblance to a real weapon is purely coincidental.)
Of course, anyone with a real interest in this new weapon system, such as a super-power enemy, has a pretty good idea what's going on anyway.
Footnote: The J20 is a Chinese aeroplane, not Japanese.

There are a few reasons you disclose a project like this:

Intimidation: You may want your adversaries to know that you have a weapon like this and exactly what its capable of.
Tax Payers: To some extent you may want to keep your tax payers happy. While not every citizen pours over the budget of their government, considering what was spent on the F-22 or current F-35 it would be hard to not show people at least a bit of what you are working on for all that money.

Now on a similar note you may not really be concerned about disclosing something like this. Keep in mind they are not disclosing the blueprints or through documentation on how the plane works. Seeing something and knowing what it can do are a far cry from designing and then physically constructing a bird like this. Take the SR-71 for example, it was in many regards not a secret but in the end of the day it was simply faster and more sophisticated than anything anyone threw at it and in its entire service history not a single one was lost and even when the enemy knew how fast it could go they still couldn't build anything to take it down.

To add to this, at some point it's just too cumbersome to keep a big project secret.  When you have several wings of F-22's with hundreds of pilots being assigned to them, along with thousands of other support troops, keeping that sort of a program secret is a massive undertaking. It might be possible to operate them the way that the F-117's did (early on), only at night & only where they were never visible to the "outside world," but it would be incredibly expensive and would impose severe limitations on how the pilots could train. At some point, the secrecy isn't worth the costs.

The purpose of an aircraft like the F22 is to make your own people feel good about having the world's best fighter (or so you claim) and to sell it to your allies.
It was never really a secret from a serious superpower enemy.


text:
May an uncertificated pilot log non-PIC flight time for future certification?
Let’s suppose I as a PIC take a friend up flying with me and this friend does not have a pilots license.  Now let’s suppose I teach him how to control the airplane and let him fly for a while.  I even go on a cross country flight and let him fly most of it.
Looking at the regulations regarding aeronautical experience for a private certificate, CFR 61.109, it states that the pilot must log 40 hours total flight time, 20 hours of instruction and 10 solo.  CFR 61.51 outlines documenting aeronautical experience and has caveats for the type of flight time but nothing for this type of situation however, 61.109 does not stipulate that all of the flight time come from solo or instruction.
So here is the question.  May an uncertificated pilot log non-PIC flight time and use it towards a certificate when another pilot lets him fly the plane as the sole manipulator of the controls?

If you are not a CFI, you are probably not doing your friend any favors by having them "train" in the right seat and without a syllabus or without clear goals. National average for a PPL is closer to 70 hours of instruction.

Hi Chris, welcome to Aviation!  Great first question!

Your friend can't log any time because he isn't licensed and qualified to fly the aircraft and assuming that you aren't a CFI then he isn't receiving training either. He's just a passenger, although if he wants to record the time for his own purposes that's fine, it just doesn't count for anything as far as the FAA's concerned.
First, 14 CFR 1.1 says that flight time is time acting as a pilot, not just time in an aircraft:

Flight time means:
(1) Pilot time that commences when an aircraft moves under its own
  power for the purpose of flight and ends when the aircraft comes to
  rest after landing;

So your friend needs to log time as a pilot. Obviously without a certificate there's no way to log PIC or SIC time, so that leaves training time. The regulations for that are in 14 CFR 61.51 (my emphasis).

(h) Logging training time. (1) A person may log training time when
  that person receives training from an authorized instructor in an
  aircraft, flight simulator, or flight training device.

I assume you are not an instructor, so no.

§61.51   Pilot logbooks.
(h) Logging training time.
    (1) A person may log training time when that person receives training from an authorized instructor in an aircraft, flight simulator, or flight training device.


text:
Is it required for pilots to contact ATC while flying VFR?

Does a pilot need to communicate with ATC while flying VFR (during departure, flight or departure) or does it depend on type of flight (like private, commercial, etc.)?
Or is it required for pilot to inform ATC only during arrival and departure for runway clearance and altitudes?
If a pilot does not remain in contact with ATC during the flight, how does ATC know what pilot's intentions are?

Which country are you asking about? The rules can be different in different places.

Being VFR does not remove your obligation to talk to ATC if you are in an ATC controlled airspace, regardless of the type of flight (personal/commercial, etc).

These questions are too broad. Answers will vary for each flight depending on where you're flying from, where you're flying to, where you're flying through etc. If you present a case (real life or simulated), you'll get better answers.

@RonBeyer - As the comment above you says, that depends on the country. In the United States (and I think Canada), VFR flight in Class E space does not require you to talk to anyone. This differs from most other ICAO countries. Now, it's a good idea to start talking on UNICOM or MULTICOM around untowered airports, which are Class E or even G, and you do need established two-way comms for any higher airspace class (which are almost always around airports) but while toodling around at 2000-3000MSL, you can keep it on GUARD and just fly.

@KeithS I'm not sure my comment differs from what you said, other than different countries. At least in the US, ATC controlled airspace you must have communication with them. Class E and G are uncontrolled (unless IFR in E). Towered airports are usually class B, C, or D when open, E when closed.

@RonBeyer - Except Class E is by definition controlled space because ATC operates there and provides IFR separation; if ATC can provide minimum services in a slice of sky (IFR-IFR separation is usually the minimum, requiring radar tracking and two-way communication with IFR flights), then it's E at least, otherwise it's G. This is why the U.S. doesn't use class F; in ICAO it's theoretically controlled but services cannot be guaranteed, which is too ambiguous for the FAA but a fact of life in other ICAO countries.

Not only is it not required (depending on airspace class: I'm assuming the question applies to the US) , there are areas of the country, like much of the intermountain west, where you simply can't contact ATC until you're at several thousand ft AGL.

It depends on which class of airspace you are flying in. For airspace classes A, B, C and D, a continuous two-way radio contact with ATC is required for all VFR flights. In airspace classes E, F and G, there is no such requirement.
The below table shows requirements for both IFR and VFR to fly in different airspace classes (source: ICAO Annex 11, Appendix 4). You should notice the second column from the right, which specified the radio communication requirements for a given airspace class.

These are general rules, that apply to all ICAO member states (basically, every country in the world), unless a specific state has decided to deviate from the ICAO standards. Such deviations will be listed in the national AIP, section GEN 1.7. For example, in some countries, two-way radio communication may be required for VFR traffic within certain airspaces classified G, even though that is generally not the case. A table with rules specific for your country will be available in your national AIP, section ENR 1.4, and will probably look quite similar to the above.
At controlled airports, a control zone will be established, which will be class A, B, C or D (cf. ICAO Annex 11 para 2.6, a control zone cannot be classified E). This means that, at a controlled airport, VFR traffic must establish a two-way radio contact with ATC, just like IFR.
At uncontrolled airports, however, this is generally not required.
During the approach, departure and en-route phases of flight, whether or not you are required to be in contact with ATC depends entirely on where you are flying. Very generally speaking, if flying close to controlled airports or above a certain level, you can expect the airspace to be controlled, and thus, contact with ATC is required. At low altitude, away from major airports, the airspace will often be uncontrolled, and no radio contact required.
The above is a very general description, and you really must refer to local charts and procedures to figure out if you are required to contact ATC in a specific area.
As a point of advice, ATC is there to help you. It is a good idea to contact ATC even if you are not required to do so, in order to receive flight information service and alerting service. This allows you to receive important information about traffic, weather, military activity, etc., and if something happens to you, a search and rescue mission can be initiated without delay.

Note: This answer is specifically about procedures in the USA; it does not apply to the rest of the world, although most countries are very similar.
It depends "where" you are flying resp. in which airspace.
The airspace is divided into types, according to the picture attached, and is an international classification. It is then up to the countries to split their airspace (including the one in the vicinity of the airfields) into the shown ones (some use just two, some use more).
On specific charts, you can see if it is necessary or not.
Summarizing, in controlled airspace (so if the airfield lies inside of an airspace class E or higher) it is mandatory.
If the airspace around an airfield is of class F (missing in the chart) or G, it is not. This is quite often the case for smaller airfields.

The chart is a bit confusing as it first says in class E you need two-way communication with ATC, with note about control tower, but then it says two-way communication is only needed if flying on IFR flight plan. The later is correct, the former is misleading (and towered airports are class D anyway).

There are also Class G towered airports that don't have the IFR weather reporting capabilities to make them Class D

Can you share your source for this chart? The graphic seems to be from the pilots handbook but not sure where the chart section is from.

Which jurisdiction is this for?  it is not correct for the UK for example.

Yeah please make sure to include the locality for which your answer is appropriate! We aren't all American.

Here are some straight-forward answers assuming you're asking about flights operating in the FAA jurisdiction.

Pilots are not required to communicate with ATC while operating VFR unless they are operating at a towered airport or within certain airspace which is usually associated with a towered airport. Take a look at chapter 3 of the Aeronautical Information Manual for more detail on airspace. I think it's also a point of confusion that not all controlled airspace requires communication with ATC. I have often told students to think of class E airspace as "controllable" airspace. ATC does not exercise control over all the aircraft in controlled airspace.
Airports without control towers have a common frequency on which aircraft can broadcast their intentions, but pilots aren't required to do so. Some aircraft don't even have radios. Towered airports will always require communication with ATC but the specific procedures vary slightly depending upon the type of airspace.
ATC often doesn't know the intentions of the pilot. If an airplane violates airspace ATC will usually try to contact them on all their broadcast frequencies or on guard (121.5). On en route frequencies it's not uncommon for ATC to give traffic advisories for controlled aircraft pointing out traffic that is not talking to to ATC.

Also it depends on airspace (FIR) regulations promulgated by States as well as airspace classifications, for example in Tehran FIR all flights (IFR & VFR) are obliged to have two way Communication with relevant ATS units for search and rescue.

Simply, NO. It differs even inside of a country. The point is, in which airspace you are (resp. the airfield is). Maybe some countries have additional rules, but the basic concept are the airspaces

Whether VFR aircraft need to talk to ATC depends on the class of airspace and country it is in; sometimes it's required, sometimes it's optional, and sometimes it's not available at all (due to distance, terrain or other factors). We'd need more specifics to give a useful answer.
If an aircraft isn't talking to ATC (whether required or not), ATC probably doesn't know their intentions. This may require them to notify other traffic of a potential conflict or even vector them away to provide extra separation. In some cases, they will notify the military, which may intercept it.

To give you a complete answer to all your questions:
AFAIK the jurisdiction does apply to all countries in the world (ICAO members). There are probably additional, national rules (which I estimate to not be a lot as aviation is quite international; only regarding the airspaces and mandatory radio-contact).

It only depends on the airspace you are in. As mentioned by others, there are 7 of them, from A to G where as A is the "strictest" and G is the least regulated one. Countries are free to split their airspace into the different classes (which often results in countries only using certain classes but not all). Radio contact is mandatory for VFR traffic in A, B, C and D. Every airspace (except E (has, but only mandatory for IFR), F and G) therefore also has a corresponding radio-frequency to contact. As a simple conclusion, only so-called controlled airfield (airfields inside of an airspace A, B, C or D) have an ATC. Others are "free to land" (there are rules which you should respect, see VAC or similar approach informations, but there is no mandatory radio-contact required; there also is no one having the permission to give you any clearance).
For more information regarding this answer, have a look at an ICAO chart or the airspace list posted by others.
Basically, he is required to contact the ATC on the corresponding frequency before entering the airspace. Additionally, some airports require you do contact them at specific points a certain time (5 minutes) before approaching (so not just before you enter their airspace). This is written on the VAC (Visual Approach Charts) of every airport and is not a "flight-restriction" but a "condition" to get a clearance to enter their airspace. Summarized: There is only obligation to contact an ATC if you want to enter it's airspace. Probably, the obligation is to call it early enough from outside, but this is an additional requirement IF you want to enter it's airspace. Stay outside and you never ever have to contact them.
That's why radio-contact is mandatory inside certain airspaces (A, B, C, D), the others (E, F, G) do not have an "ATC". The only possibility to switch the frequency of your current airspace is on approval by the ATC (which sometimes makes sense, imagine you want to cross a neighboring airspace: you first have to contact that one before you can enter, but you're still in your first one. In this case, the ATC you are in will allow you to change frequency). As the pilot talked to the ATC before, the ATC knows know very well (even dough they are not on the same frequency anymore) what he is going to do.

For all the people complaining about the wrong rules of the airspaces: If you want to know them exactly with all the details, please refer to one of the posted pictures, my answer is regarding to the question of mandatory VFR radio-contact. Nothing more and nothing less.
edit: airspace E does not have mandatory VFR radio-contact.

Which jurisdiction is this answer for? It doesn't apply to the US, at least. Of course, the OP hasn't said what country he's asking about anyway

What part of my answer does not apply to the US? The jurisdiction is for the European aviation but should AFAIK also apply to the US regulations.

The US has no class F, doesn't require radio contact in class E, and has no VACs.

Regarding class F: just because it exists, it is not required to be used. Many countries in Europe just use a part of the classes. AFAIK Italy, as an example, only uses A and G. But I will point this out in my answer.
Regarding E, I made a mistake which I already corrected.
The VACs are a surprise to me, but it seems to have some similar "airport information" plates, right?

Yes, there are airport diagrams and so on, but I don't know of any equivalent to a VAC's mandatory VFR reporting points. But they may exist somewhere, there are a lot of local procedures out there. It isn't a typical thing, though.

This answer is not factually correct. For example, you state that ATC service is not available in class E airspace, which is false - in fact, IFR traffic is subject to an ATC clearance in class E airspace, thus, ATC service is available (for VFR as well).

@Hougaard, I corrected the availability of ATC in airspace E. Anyway, the question is regarding mandatory radio-contact under VFR, so it's an unimportant point. And therefore I do really not care for any IFR ATC clearance but rather stick to the question.

@Pondlife, sure, there may is not an equivalence as the reporting points. That's what I stated. In some cases there are. Not in every case. And as you stated correctly, local procedures may come additionally to the airspace rules.


text:
Are there any regulations about the distance between destination and alternate airports?
I didn’t notice any distance regulations or recommendations regarding how far away an alternate airport may be. However, it is reasonable that,

Too close: The weather between the two is likely to be similar. If you are unable to land in one, you are unlikely to land the other.
Too far away: The fuel reserve is a concern, and we lose the purpose of the trip.

I've had this thought myself and I think the answer is technically no (happy to be shown otherwise). However, you can't nominate an alternate that would itself need an alternate, so that covers your weather scenario. And if you don't have enough fuel to get to an alternate without breaking minimums then you can't nominate that one either.

It's not distance as much as time. 45 minutes flight time for a cessna 172 is totally different than a 737.

If you are close to a mountain, the other side of the mountain may be quite close (in flight time) but the weather quite different (low clouds on one side)

@Ben. Your statement isn't exactly correct: if LAX and ONT are both 1000/3, either airport as destination requires an alternate, and each one qualifies as an alternate for the other.

It's not unusual for the west side of the SF Bay Area to be socked in with a low marine layer, and 10 miles east to be CAVU.

On an IFR flight plan, 14 CFR 135.233 requires

§ 135.223 IFR: Alternate airport requirements.
(a) Except as provided in paragraph (b) of this section, no person may operate an aircraft in IFR conditions unless it carries enough fuel (considering weather reports or forecasts or any combination of them) to—
    (1) Complete the flight to the first airport of intended landing;
    (2) Fly from that airport to the alternate airport; and
    (3) Fly after that for 45 minutes at normal cruising speed or, for helicopters, fly after that for 30 minutes at normal cruising speed.

Constraining from the other side, 14 CFR 91.169 requires

(c) IFR alternate airport weather minima. Unless otherwise authorized by the Administrator, no person may include an alternate airport in an IFR flight plan unless appropriate weather reports or weather forecasts, or a combination of them, indicate that, at the estimated time of arrival at the alternate airport, the ceiling and visibility at that airport will be at or above the following weather minima:
    (1) If an instrument approach procedure has been published inpart 97 of this chapter, or a special instrument approach procedure has been issued by the Administrator to the operator, for that airport, the following minima:
        (i) For aircraft other than helicopters: The alternate airport minima specified in that procedure, or if none are specified the following standard approach minima:
            (A) For a precision approach procedure. Ceiling 600 feet and visibility 2 statute miles.
            (B) For a nonprecision approach procedure. Ceiling 800 feet and visibility 2 statute miles.
        (ii) For helicopters: Ceiling 200 feet above the minimum for the approach to be flown, and visibility at least 1 statute mile but never less than the minimum visibility for the approach to be flown, and

The maximum distance for an alternate airport is limited by your aircraft’s fuel range, but practicality (not losing the purpose of the trip) will tend to be more constraining than math. The minimum distance depends on the weather.
Considering it from this perspective, given that the objective is safety, stipulating “at least X but no more than Y units of distance” would be inappropriate for similar reasons as to why we tend to think of fuel in terms of time rather than length.

authors: Кирилл Картмон


text:
How many types of tape do airplane mechanics use?
I was reading this blog linked from this answer, and it mentions

“We never use, and don’t even stock, duct tape,” explains a veteran
  airline mechanic. “Some of the tapes we use cost hundreds, even
  thousands, of dollars per roll.

Which brings up the question, how many types of tape are used by airplane mechanics and what are they all used for? Obviously speed tape is one type and duct tape is not, but what else is there?

Here is a selection of fine tapes, each for a special purpose. At the other end of the scale, lots of masking tape is used for paint jobs. I doubt that there is a single aircraft flying which does not have some sticky tape somewhere.

@PeterKämpf -- if nothing else, you have Mylar or Kapton insulating tapes in switching power supply magnetics ;) (heck, even your cell phone charger has tape in it ;)

@UnrecognizedFallingObject: Right, two layers at least. I did not even think of electronics, but you are absolutely right!

When I was flying Cessna's we called it 100mph tape.  Now I'm flying Boeings and we still call it 100mph tape.

We called it 500 MPH tape. I was a pilot flying off the USS Nimitz in the Mediterranean. The salty  environment was very corrosive and we would fly the aircraft off regularly to undergo inspections ashore in Sigonella where we had a detachment. Apart from that, and regular corrosion control practiced on the ship, we were asked to fly through rain if we had the chance. We used Duct tape on the leading edges of the wings to keep the paint from getting chipped by the drops of rain.

I can't speak for General Aviation, but based on the number of tapes I've seen, it wouldn't be outside the scope of reality to think the aircraft manufacturers have a partnership with 3M to come up with as many different types of tape as possible.
For wiring repairs alone, I know our shop keeps at least 20 various types of tape on hand in our bench stock area to grab in a hurry. There are probably another 20-30 other types of tape we may use in rarer situations, but don't keep on hand. We'll usually order that on an as needed basis.
There are a number of different types of "Speed Tape" as well. These are commonly used as very temporary structural fixes for small holes, dents, etc... on certain parts of the aircraft. It looks a lot like a sheet of aluminum foil, but it's some of the stickiest stuff I've ever dealt with.
I know we also have different Mylar tapes that are used for a number of different applications. One of the applications, in particular, is when floor panels are sealed. The sealant can take 24-30 hours, in some cases, for a tack free cure. Since we want to use the airplane sooner, we can cover it with Mylar tape. It'll allow it to cure while under the tape. After the cure, we'll simply pull the tape up and continue business as usual.
There are a number of other specialized tapes I've seen for various other applications. I do know that I have seen duct tape on bleed duct insulation. This is rare, but sometimes the insulation gets torn and people use duct tape to repair it. Quite frankly, I've never stopped to look and see what the approved tape is for that, but if there was one and only one application for duct tape, that might be it.
I can't offer you an exact number, but they most certainly number in the hundreds if not thousands! Oh, and one other thing I've noticed is that Boeing tapes are usually different than the tapes specified by Airbus! So, each manufacturer has chosen certain tapes for certain applications and purposes, although some are interchangeable.
If you really wanted to get crazy and technical, each tape comes in different widths too. All of these come in standard widths of 1/4", 1/2", 1", 2", and 3". I'm sure there are other width's too, but I know I've seen all of those sizes.
Quite frankly, it's dizzying and unbelievable how much tape is on an airplane!

Most of which could probably be replaced with duct tape ;)

If you search a leading manufacturer's website for "aerospace", it will come up with more than 500 products. And if you go glider flying, look how they seal the gaps between wing and fuselage. Or the aileron gaps. And so on.

@TomMcW If it can't be fixed with duct tape, you're not using enough :)


text:
How do you calibrate the compass of an aircraft on a compass rose?
A follow-up from this question; one of the answers mentioned that the compass rose in the picture was used to calibrate an aircraft's compass.
But how does that actually work? Do you park the aircraft on top or something?

@RonBeyer Yeah, that was my impression as well: the compass would be pre-calibrated outside of the aircraft, so the only thing you would really be able to do on the airfield is double check its right. But even with that, I don't see why you can't double check with just a hand-held compass

For a magnetic a compass, a card is completed with the error for each cardinal point.  The pilot takes that error into account when setting the heading.

Usually completing the card is better left to the A&P, not something I'd attempt to accomplish before a flight. I'm not sure that the pilot is allowed to adjust this anyway? (I was wrong in my comment before, it is adjustable).

@RonBeyer A compass swing is indeed an A&P maintenance item. Technically a non-A&P rated pilot can't even do the last step of checking the error and filling out the card without a sign-off from a certificated mechanic. The compass swing is generally a two-person job anyway though (one person taxiing the plane into position, the other verifying it's properly aligned on each heading from outside).

@DavidGrinberg It's surprising (and a little depressing) how "wrong" a regular hand-held compass can be: If you take one up in a small aircraft and move it around the cabin you can find  variations of 10 degrees or more depending on where you hold it. The flux-gate compasses in many modern cell phones (like the iPhone) can also give variable results (if anything they seem easier to upset, even after doing the "calibration" dance the device insists on).

I know also one plane repair workshop where there's a huge turnable circle where you park the aircraft on and then a small motor turns the aircraft with the aircraft on it. There, a laser is mounted on the aircraft that points directly to the front of the aircraft and then the laser points on the wall on a big scale what the exact orientation of the aircraft is. Definitely one of the most unusual parts of aircraft maintenance I saw so far!

Most aircraft compasses include compensating magnets to correct for installation error (due to natural magnetic fields in an aircraft from steel parts and electrical equipment). When installing a new compass or performing significant electrical work on an aircraft the compass may need to be re-calibrated and the compensating magnets adjusted (typically by turning small screws, like the ones shown below).

There are several ways to calibrate (or "swing") an aircraft compass - the use of a properly-surveyed compass rose constructed to applicable FAA standards and marked on an airport is one of them, and ensures the compass swing is being performed in an area free of magnetic disturbances which should result in an accurate calibration.
The basic procedure is to taxi the aircraft to the compass rose and align it with the compass directions using a combination of the ground markings and a "gunsight" compass. A full description of the procedure can be found in AC 43-13.1, Chapter 12-37 ("Compass Swing"), but the quick-and-dirty version is:

Taxi out to the compass rose and align the aircraft so it is pointing toward Magnetic North.

Adjust the compass compensating magnets so that the compass reads North.

Turn the airplane so it is pointing toward Magnetic East (090).

Adjust the compass compensating magnets so that the compass reads East.

Turn the airplane so it is pointing toward Magnetic South (180).

Adjust the compass compensating magnets to remove one half of the "South" error.

Turn the airplane so it is pointing toward Magnetic West (270)

Adjust the compass compensating magnets to remove one half of the "West" error.

Once the compensating magnets have been adjusted a Compass Deviation Card is prepared to inform the pilot of the remaining compass error.
Beginning with Magnetic West (270) turn the aircraft to align with each of the 30-degree lines on the compass rose (270, 300, 330, North, 30, 60, 90, 120, 150, 180, 210, 240), and the error is recorded on a compass deviation card similar to the one shown below.

A compass reading within ±10 degrees on each 30-degree heading marker is considered acceptable per AC 43-13, and better results are usually achieved.
The compass swing is typically performed with the engine and electrical accessories (radios) running per AC 43-13. Some mechanics may also perform a second swing with radios off, and include an alternate deviation card for that configuration.

Note that not all aviation compasses have integral compensating magnets. For those that don't you generally skip right to the end and fill out the compass deviation card. If it's within acceptable limits no further action is necessary, if not external compensating hardware ("compass balls") can be used, or the compass can be replaced with one that has compensating magnets. Compass balls are also used with compensating compasses if they can not be brought into calibration using the compensating magnets.

Are compass balls like mouse balls?

@FreeMan the ones for aircraft are about that size actually. They're the little cousins of Kelvin's Balls that you'll find on marine vessels for the same reason.

A clever way to alight the aircraft is to put both wheels on the desired radial line that is orthogonal to the desired heading.  For example, if you put both main landing gear exactly on the 270 radial line with the right wheel on the inner part of the radial circle, then your aircraft is pointing north (orthogonal to the 27 radial line).  You can repeat this procedure for each radial line to get the desired heading.  This works particularly well for a high wing aircraft such as a 182.  For a low wing aircraft you could use a spotter outside the aircraft to help determine when wheels are on the line.


text:
Why aren't planes loaded from both ends?
Related to this question about plane loading efficiency, if planes have multiple entrances (generally 6 or more) why are planes not loaded from both ends? I think I've seen it happen sometimes, but the majority of my flights are on 737s and are just loaded from the front entrance.

Sometimes planes are loaded from both ends. Burbank Airport has no jetways and stairs are usually placed at both the front and back of the aircraft (they have wheelchair lifts for passengers who need them). JetBlue sometimes does this elsewhere as well.
At most airports with jetways, boarding occurs from at least the second floor of the terminal building. That means that passengers who take stairs down from a rear exit would have to climb back up into the terminal, which is inconvenient.

It's also fairly common to have two sets of stairs when aircraft are parked at remote stands and passengers are bussed to/from the terminal (more common in Europe and Asia, generally rare in the US).

As an aside, for double-aisle and multi-level aircraft, it's common for them to be boarded via 2 or even 3 jetways. When 2 jetways are used, they're usually attached to the 1st and 2nd left-side boarding doors on the first level. When three are used, it's usually those two plus a door on the second level. Getting a jetway around the wing is not practical though, which is the main reason why aircraft boarded from jetways usually don't load from the back.

A related question appears to be why planes aren't loaded from the middle. The real bottleneck isn't the single jetway, it's the crowded aisles. If you had a door just in front of the wing, up to a third of the passengers could move forwards.

JetBlue at LGB also boards and deplanes in the front and back. Whenever I fly there, I try to book one of the last seats on the plane. Everyone is always so pleasantly surprised that they aren't going to be the last people on the plane! Consequently, there is always a little bit of confusion in the back of the plane, especially when people have put their luggage closer to the front.

Where do you live? I would say its more common that planes are loaded from both the front and rear than to only be loaded from the front.

@Scott That's definitely not more common in the U.S. That's usually only feasible in places that don't have jet bridges (i.e. where you board via stairs from the ramp.) The vast majority of airports use jet bridges these days.

@ reirab - most times I fly there is a jet bridge from the front and the peasants in the back have to climb down some stairs and walk across the runway. Still better than waiting for an entire plane to leave one door. (Flynig from and/or to Australia)

The aviation industry is already running at near-peak efficiency, performing crucial tasks simultaneously to ensure quick turn-around.  Trying to speed up the boarding process by allowing entrance from both ends would be doable with a large amount of changes to the existing process, in both operations and infrastructure.  However, the result would be horrendous and time- and resource-consuming at worst and comical at best.

Jetways need to be able to reach all points of ingress/egress, where currently, they only reach the forward doors.  Seeing as aircraft nose-in at the gate, to reach the aft doors would require a jetway that goes around the wing (above the wing is even less practical from a design/physics standpoint), effectively creating an even smaller limit to the size of the aircraft that can fit at the terminal since there is now a jetway that needs to reach the rear doors.  As you can see, the space between aircraft is already tight:  Or, you use a simple stairway at the aft door and allow passengers on the tarmac, an already busy place during aircraft turn-around, and we don't need them touching anything en route.  I highly recommend against the latter.

In many instances, during boarding, the rear and/or opposite-side doors are already in use for loading/unloading food and drinks and taking out the trash.  So you'd have to redesign that process.

Humans are generally stupid in large groups.  Southwest notwithstanding, your typical airline assigns seats.  Imagine a passenger entering the rear door with seat 1A.  It doesn't have to be that extreme.  It can be any seat assignment more forward than another passenger coming the opposite direction down the aisle, which has the effect of halting both directions of travel.  Passengers already sit in the wrong seats, or travel with babies, or carry too much luggage (or stow it selfishly).

There have been many studies on efficient boarding methods.  The most efficient algorithm seems to be the Steffen Method, but this method requires someone with an inordinate attention to detail (and willing passengers) to line people up in a specific order.  Taking into account crew resources, the most efficient method is by window-middle-aisle groups, then by random order (i.e. "single-zone"), with typical "zone boarding" least efficient.
EDIT:
There are scenarios where boarding from both ends makes sense and is feasible, e.g. smaller planes with fewer passengers.  On larger aircraft, the problem compounds itself as the number of passengers grows, each "collision" incident affecting that many more people in the queue.  Minimizing collisions requires airlines to throw more resources at the problem, namely personnel to direct traffic.  Ask any CFO - more often than not, human resources is the most significant slice of the operating budget.
In any case, engineering a solution should not entail best-case scenarios; it should be designed for typical-case at best, and more commonly for worst-case.  The human factor is one that cannot be overlooked.  There is no such thing as an idiot-proof system.

Also keep in mind that any jetway has to get out of the way for the plane to move in or out of the gate, which takes up even more tarmac space around where people are working on the plane next to the one leaving.

Under the tarmac?

cost-prohibitive.  digging up the ground (tunneling) is monumentally more expensive than building a bridge.

Well, there is always somebody at the gate who checks the boarding cards and can direct the passengers to the right corridor. If bus and stairs are used, there often are two stairs and the flight attendants sometimes stand by the bus and direct people like that.

"Imagine a passenger entering the rear door with seat 1A." - two boarding zones. Front passengers (1 to 15) and back (16 and higher).

what you describe is a perfect scenario.  someone will board from the wrong door.

I have often seen boarding happening from both ends, front and back on smaller aircraft's at airports with bus boarding. Usually security at the front will allow in only rows 1-15 and at the back 16 onwards. (they will stop you before you climb the stairs)

not surprising and easily doable due to the small pax count.   i haven't run any numbers, but i imagine that time spent in boarding scales at best O(n^2) for n passengers.  any algorithm for more-efficient boarding needs to consider not only time, but crew workload as well, which is why dr. steffen's method is unrealistic.

EasyJet A319/A320 planes in Prague Vaclav Havel (PRG) are usually unloaded using the bridge, but loaded through the bridge only until row 15, people sitting in row 16 and behind and sent on the tarmac and loaded through the moving stairs in the back door. The reason they seem to give is not that it's faster to get on the plane, but it's faster for all the people to organize themselves, put the baggage where it belongs, sit down, etc. They rarely refuel or do more-than-necessary maintenance in PRG, so loading the passengers is a limiting factor, as well, there's enough space on the tarmac.

@yo' - they definitely refuel in PRG.

@JonStory One of the plane's routes is LUT-PRG-CDG (LUT is EasyJet's base) and I'm sure that once I observed the plane from gate arrival until I loaded myself into the plane some 15 minutes before pull-out, and I didn't see any tanker on my side of the left side of the plane (I can't 100% speak about the right side). Both legs are very short, so I suppose they get fuel at home for both legs at better price.

Dulles (outside Washington DC) at one point intended to have passengers loaded via "mobile lounges" [buses with scissor lifts].  I would guess that if planes didn't need to load and unload other cargo, such a design could improve turnaround time, but as it is planes overlap the time they spend loading/unloading passengers with time spent doing other necessary tasks.

Typical "zone boarding" does not occur in real life because passengers do not line up in order like robots. Random boarding did pretty well, and is the one passengers prefer because they get to do what they want. I expect that adding in a moderate amount of rear-to-front bias is an improvement on random boarding, which is precisely the boarding scheme the airline achieves by asking people to board in zones.

@erich People in the rear boarding from the front door (because they aren't familiar with the new boarding procedures) won't make it any slower than the current system. People in the front are unlikely to board from the rear door, because people are lazy and that would mean walking farther.

@immibis People in the rear boarding from the front door will cause headaches. Suppose the aircraft has 30 rows and I'm sitting in 23C. I head to the rear door and board from there. Another passenger in 28F has boarded via the front door. We're standing in the aisle blocking each other, and passing in a narrow aisle when we both have roller bags is challenging at best. Meanwhile everyone else is stuck in both directions.

It's worth noting that while the rest of the operations on the tarmac and at the terminal may be near "peak efficiency" the process of boarding the aircraft is empirically about as inefficient as we can make it (see here from Bloomberg Business, this delightful Mythbusters segment).

@voretaq7: as a sum of all parts.  also see peter's response noting that it's not much worth it to speed up one process (boarding) only to still wait on the other processes to finish.

Regarding the Steffen method, it doesn't really actually require anyone with an inordinate attention to detail. It only requires a computer with inordinate attention to detail (which is easy for a computer) to assign boarding positions based on the Steffen method and then something like what Southwest already uses to get people to actually line up in that order. In my experience, this seems to work reasonably well for Southwest. It's much more orderly than Delta's boarding process where many people don't seem to understand that Zone 1 is actually the third boarding zone.

@voretaq7: The mythbusters experiment used the same passengers every time.  If they didn't shuffle the seat assignments every time, people would start to make local optimizations.  Also, getting your plane-boarding skills warmed up in general will probably speed later runs, as you've already figured out exactly how your bags fit in overhead bins.  I bet a 2nd run of zone boarding would also have been faster than their "control", even if they did reshuffle seat assignments.  No idea whether this would have been enough to make it faster or more pleasant than any of the other methods.

I don't  know the physics involved. Is the entire process free from regulatory oversight?  The cognizant regulator (if there is one) turns a blind eye to the boading/deboarding of passengers and lets the chips fall where they may?  Or do the regulators get involved with how things need to be done?

I'm not sure, but I think this is somewhat a geometry thing. If planes are being loaded from a jetbridge, it would have to get past the wing to reach the rear door. That would involve it having to drive around the wing to get to the door, which is somewhat space-intensive, and also requires a pretty long jetway with limited ability to have supports along its length (since it has to deal with different wing sizes). On planes with multiple front doors along one side, it's not that uncommon to see them being used, whether they're on different levels or there's just a door at the front and another door in front of the wing. There, it's just a matter of how many jetways the airport has at the gate, but they don't have to drive around the wing.
When planes are being loaded or unloaded away from the airport, it's not uncommon to load/unload from the back as well as the front; there, they just have to use two mobile lounges (at IAD) or airstairs (just about anywhere else).

This is the primary answer. We like jetways and getting a jetway around the wing is not feasible while parking aircraft perpendicular to the terminal. Parking parallel to the terminal would both be difficult to maneuver and take up too much space per aircraft. If you want a really good idea of how dense aircraft parking at terminals can be, take a look at Atlanta.

Atlanta should never be used as an example, on account of the fact it's an inherently silly airport with an underground train. The sooner Hartsfield-Jackson accepts that it's a theme park, not an airport, the better.

Some lowcost airlines use both ends to speed up both loading and unloading the passengers. Moreover, for huge aircrafts (A380 and B747), you may use several jetways

This is common for Ryanair in Europe.

It's very common for most European low-cost airlines.

This is always done with two stairs, (not a jetway and a staircase) and generally away from the terminal building to avoid congestion at the jetways. I suspect that, besides the increased height, larger planes have increased probability of a disabled passenger, which would make stairs not an option.

@steveverrill Yes, having more passengers increases the probability that you have one who can't use stairs. But boarding by stairs is, as Jon Story says, very common for European budget airlines and they must have some method of getting people who can't use stairs onto the plane.

@steveverrill: as a side note I had a few cases where the passengers were leaving the plane via the jetway and stairs (and meeting at the top of the tower - the stairs ones needed to climb up)

@DavidRicherby, there are mobile lifts that are used for disabled passengers.

@steveverrill I think the question is not restricted to jetways. I've already seen passengers boarding via jetways whereas other board via stairs at the same time (it was in Spain, I should have taken photos to illustrate my answer). And yes, it was on a European budget airline.

authors: مودي الدوسري


text:
Is there any reason to use only UTC standard time in aircraft and not GMT?
Why are we not using the GMT time standard in an aircraft? Why is only UTC the standard on-board?

No place in the world actually observes GMT, except some astronomers. The British will tell you, out of habit, that they observe GMT in the winter but actually their clocks all tell time in UTC.

@hobbs: I'd wager that most clocks in Britain deviate from GMT and UTC by significantly more than GMT and UTC deviate from each other.

@hobbs You'll find it referred to as GMT because that's the legally defined time zone that we consider ourselves in. It's not wrong and it's not a bad habit.

What makes you think UTC is the time reference for an aircraft? Reference for what? (avionics?). I would except GNSS time to be used too.

UTC is in principle the same as GMT.
But for accurate applications there is a difference:

Saying "GMT" often implies either UTC or UT1 when used within informal or casual contexts. In technical contexts, usage of "GMT" is avoided; the unambiguous terminology "UTC" or "UT1" is preferred. Wikipedia

UTC: Is defined by atomic clock with corrections for leap seconds added manually.
UT1: Is defined by the Earth's rotation, hence is more susceptible for change and less easy to calculate than an atomic clock.

However the difference between the two is less than one second. It might matter for your $8000 \frac{\text{m}}{\text{s}}$ satellite or for your $300 \frac{\text{m}}{\text{s}}$ aircraft, but otherwise your can consider them equal for informal applications.

if it is more accurate than the GMT , then why we are not adopting it in an area where precision is matters..if you don't mind , could you please state the difference..am pretty much curious to know about that.

"GMT" is solar time: seconds are noon-to-noon divided by 86400. Earth's rotation isn't constant, though. "UTC" is a count of atomically-defined seconds, which are constant. A UTC day is 86400 or, rarely, 86401 of these, always within 1 second of GMT.

Picking nits: are as close to constant as is possible given our current state of technology...

@NikhilKumarM Aviation "Zulu Time" IS UTC. GMT hasn't been used in aviation (or any other field I can think of where timekeeping is critical) in several decades. While some people may persist in calling UTC GMT (because the times are equal) they are being imprecise in their usage, and should be using the correct term.

@NikhilKumarM We do adopt it, pretty much everywhere. I have actually never seen a modern application where GMT was used as a universal time standard; all it is is an old, obsolete name that people sometimes use. When someone says "GMT" for a universal time standard, they probably mean "UTC."

@rgeorge, a UTC day can also be 86399 seconds long, although it's never happened yet.

@rgeorge GMT is a mean solar time, averaged over the year.  It's absolutely not noon-to-noon divided by 86400 - that would vary far too much throughout the year.  The clock time of solar noon varies by around half an hour from one time of the year to another, because of the combination of the eccentricity of the earth's orbit and the tilt of the earth's axis.

I'm not sure I understand. Under what conditions do you need to specify a time with more accuracy than 1 second?

@CGCampbell and the state of technology, since the 1960s, is that our clocks are more reliable than the rotation of the earth itself :)

GMT (Greenwich Mean Time) is a time zone, observed by the UK and Portugal in winter and by Iceland and a number of African countries.
UTC (Coordinated Universal Time) is a time standard, defined by an atomic clock. It is kept synchronous with the solar time by adding (or removing) leap seconds.
In the GMT time zone, the time is equal to UTC.
Before UTC was defined, GMT was the international reference time, called 'Zulu-time'.

We still use Z for Zulu in aviation to indicate UTC in flight plans, clearances, and weather

Because the earth's orbit varies, the value of a GMT second varies. Technological development, especially the advent of computers required the use of a constant second, not a variable second. GPS, for example, requires the use of a constant second, as do all sorts of aviation related equipment.
The history of developing a non-varying standard second is involved to say the least, but in the end the time it takes for a Cesium-133 atom to oscillate 9,192,631,770 times was chosen as the definition of a UTC second. Atomic clocks around the world are coordinated to keep UTC.
Usage of astronomically determined time as the world's standard for technical purposes stopped on January 1, 1972 (as I remember) except for the purpose of updating UTC. Whenever UTC differs from UT1 (the current astronomically determined time) by 0.9 seconds, a leap second is applied to UTC. Thus GMT and UT1 never differ by more than one second.
The world's time zones are all assigned a letter. U is the letter assigned to my time zone (UTC-8, in Oregon), Z to the time zone the center of which in the prime meridian at Greenwich (UTC-0).

The "mean" in GMT refers to the time being averaged over the year, such that noon in Greenwich on average falls at 12:00:00 GMT, but varies significantly from this during the year due to the eccentricity of Earth's orbit, etc. It is, as noted in other comments, not a technically maintained timescale these days, more a historical ideal. The averaged-between-multiple-observatories time standard you speak about is Universal Time, usually in the technical incarnation called UT1 -- which is indeed the target for determining leap seconds in UTC.

@HenningMakholm Thank you for the information. I've corrected my answer.


text:
Which aircraft are 76A, 76B, 77E, 77F?
I have a list of of aircraft types like so:
0      320
1      76B
2      DH4
3      E95
4      319
5      76A
6      321
7      77F
8      CR9
9      77E
10     OAAG

I was able to identify most of them:

320: Airbus A320
DH4: Bombardier DHC8-Q400/Q400CC (DH4)
E95: Embraer ERJ-195
319: Airbus A319
321: Airbus A321
CR9: Bombardier CRJ-900

However there are some that I cannot understand exactly which model they are. I guess they are Boeing 767 and 777 but I am not sure which model.
Can you help me out to find out which aircraft are these:

76A
76B
77F
77E
OAAG

Where did you get the list from? As far as I can see, the codes are neither ICAO nor IATA codes.

These are mostly IATA type designators, except for OAAG, 76A, 76B and 77E.
77F is the official IATA designation of the freighter version of the 777.
The rest:
77E seems to be an internal designation used by British Airways for a specific sub-fleet with an increased gross weight.
76B seems same as above just for 767-300ER.
I wasn't able to find anything about 76A (but I'd guess that same as above) and OAAG (perhaps it is part of the registration of an individual aircraft)

For most accurate information, you can check the following link
from: IATA PART 2 — AIRCRAFT TYPE DESIGNATORS (DECODE)
As noted in previous answers, 76A, 76B, 77E and OAAG, those are not IATA aircraft codes, hence must be some internal codification for some airlines.
Also wikipedia offers a best view of the whole list here but for latest information, the first link comes direct from IATA's site (most updated and reliable version).
Best,

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Is there truly no way to get information about medical application status?
I had an event in 2005 that has not happened in the 10 years since.  When I went for a 3rd class medical the AME I went to seemed very skittish and wanted to send my records to Oklahoma City for review.  They received them the first week in March.
As we near the two month mark I have called and asked for a status once each week and have been struck by how little information they provide.  My application, for example, has been in the "handed over to the Doctors" status for almost a month with no new notations on the file.  This means I can't tell if it is sitting in the queue waiting to be processed, or is actually being processed by a Doctor who just isn't putting any notations in.  If I'm in the queue I have no way of knowing whether there are two or two hundred apps in front of mine.  In short, calling and checking the status is a worthless exercise.
In every organization I've ever dealt with there was always some way of going up the chain and getting some kind of information.  I'm told by the call center reps that is not possible.  I wanted to verify that information with the community here, though... is this just the way things are?  Is there no way whatsoever to get some useful information?  If anyone has been down this road and has tips they would be greatly appreciated.

Have you been in touch with AOPA's medical people?

@casey, I only recently joined the AOPA as a student pilot so I wasn't completely aware of all the services they provide but this is a great suggestion.  Thank you!

Dealing with the FAA medical is always a tiring process. Best places to consult would be services like AOPA medical assistance, or through Aviation Medical Advisory Service (AMAS).
There are other options probably, but I know AMAS is the go to consulting group for controllers and a lot of airline pilots. AMAS will often help guide you with knowing ahead of time what information you need and what forms to have filled out to try and make the process go quickly.